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Chapter 13 Crime and Accident Reconstruction

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1 Chapter 13 Crime and Accident Reconstruction
© 2012 Cengage Learning. All Rights Reserved

2 Introduction—Objectives
Discuss the contributions of various forensic specialists to crime reconstruction. Discuss possible motives for crime-scene staging. Discuss the factors involved in a motor vehicle collision. Describe the five levels of an accident investigation. Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

3 Introduction—Objectives
Compare and contrast skid marks and yaw marks. Explain the importance of the law of conservation of momentum and law of conservation of energy in accident reconstruction. Evaluate factors that can lead to incorrect reconstruction. Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

4 Introduction—Vocabulary
contact damage—damage to a vehicle caused by contact with an object or other vehicle law of conservation of energy—rule that states that energy is neither created nor destroyed, but it can be converted into different forms law of conservation of momentum—rule that states that the momentum of a system remains unchanged unless a force acts upon it Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

5 Introduction—Vocabulary
reconstruction—in criminal investigations, the process of recreating the actions and circumstances based on examination and interpretation of evidence skid marks—marks left on the roadway by the tires when the driver of the vehicle applies the brakes suddenly staging—the intentional altering of a crime scene in order to disguise what really happened yaw marks—skid marks in a curved path as a result of an out-of-control skid Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

6 How Many Motives for a Murder?
July 4, 1954 Marilyn Sheppard was murdered in her bedroom Husband, Samuel, became the chief suspect after knowledge of an affair became known Samuel was tried and convicted of murder On appeal, Dr. Kirk reconstructed the crime scene to prove that a third person was there Conviction overturned 6 Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

7 Introduction Reconstruction—the process of reproducing the actions and circumstances of an accident or crime based on examination and interpretation of evidence. Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

8 History (Obj 13.1) Dr. Hans Gross—authored textbook on systematic methods for analyzing facts of a criminal case Dr. Alexandre Lacassagne—advocated combining science with criminology Dr. Edmond Locard—exchange principle Edward Heinrich—forensics requires broad knowledge in many fields of science Dr. Paul Kirk—a dissertation described principles of crime reconstruction Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

9 Role of Evidence Reconstructionists use evidence to:
Establish a timeline of events and relationships Connect victims and suspects involved in the crime Example: shoe tread Size Shape Pattern Depth Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

10 Crime-Scene Staging (Obj 13.2)
Reconstructionists must be aware that crimes may have been staged Staging—the intentional altering of a crime scene in order to disguise what really happened. Making crimes appear to be: Suicide Accident Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

11 Accident Investigation (Obj 13.3)
Level 1: Reporting Level 2: At-the-scene investigation Level 3: Technical follow-up Level 4: Accident reconstruction Level 5: Cause analysis Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

12 Reporting (Obj 13.4) Level One Collecting basic information Facts
No opinions Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

13 At-The-Scene Investigation (Obj 13.4, 13.5)
Level Two Photographs and Measurements Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

14 Coefficient of Friction
Coefficient of Friction—a quantitative value, determined through experimentation that measures the roughness of a surface. s2 = 255df s = speed of travel (km/h) d = distance (length) of skid mark f = coefficient of friction Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

15 Coefficient of Friction
Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

16 Examinations Was alcohol a factor?
Contact damage—damage on a vehicle made by another object or vehicle Equipment failure Occupant restraints Maintenance of tires, air pressure, headlights, taillights Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

17 Technical Follow-Up (Obj 13.4)
Level Three Used when a crime has been committed Prepare a map of the crime site Interview witnesses Assess visibility at the site Evaluate evidence (e.g., paint chips) Toxicology report Autopsy report when there’s a fatality Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

18 Accident Reconstruction (Obj 13.4, 13.6)
Level Four Law of conservation of momentum —rule that states that the momentum of a system remains unchanged unless a force acts upon it —energy cannot be created or destroyed, but can be converted from one form to another Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

19 Law of Conservation of Momentum
Work (w)—the amount of energy transferred by a force (F) acting through a distance (d). w = F x d Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

20 Newton’s Laws of Motion
First Law—Law of Inertia a) an object at rest will remain at rest, and b) an object in motion will remain in motion with a constant velocity unless some external force acts on the object Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

21 Newton’s Laws of Motion
Second Law—expresses the relationships among acceleration (a), force (f), mass (m) Third Law—for every action, there is an equal and opposite reaction Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

22 Law of Conservation of Momentum (Obj 13.6)
Momentum (p) = Mass (m) x Velocity (v) p = m x v Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

23 Cause Analysis (Obj 13.4) Level Five
Experts share in court, based on facts and research, how and why an accident occurred Conflicting analyses are possible Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

24 Forensic Science II: Crime and Accident Reconstruction, Chapter 13
© 2012 Cengage Learning. All Rights Reserved

25 Pitfalls of Reconstruction
Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

26 Chapter Summary Several forensic investigators contributed to the acceptance of crime reconstruction as a scientific, logical, and objective process. Evidence helps crime reconstructionists establish a sequence of events leading up to the crime as well as relationships between the scene, the victim, and the suspect. Forensic investigators and scientists rely on analysis of evidence as well as witness accounts to recreate or reconstruct a chain of events. Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

27 Chapter Summary Staged crime scenes are usually an attempt to cover up a murder or insurance fraud. All accidents must be reported at level one, but accidents that require research and potential litigation require all five levels of investigation. Skid marks and yaw marks help investigators determine the speed at which a vehicle was traveling prior to a collision or accident. Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

28 Chapter Summary Investigators use the law of conservation of momentum and the law of conservation of energy to determine initial velocity of the collided vehicles. The three main causes of accidents are: Environmental factors Human factors Vehicular malfunction To ensure the validity of reconstruction avoid flaws in logic Forensic Science II: Crime and Accident Reconstruction, Chapter 13 © 2012 Cengage Learning. All Rights Reserved

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